A decay series Often the product of one radioactive decay is also radioactive – this produces a radioactive decay series Try and work out the ??????s
Decay Series A decay series occurs when one radioactive isotope decays to another radioactive isotope, which decays to another, and so on. This allows the creation of nuclei that otherwise would not exist in nature.
1 mole would have a mass of 238 grams 1 mole would have a mass of 238 grams. 1 mole contains 6 x 10^23 atoms so the mass of one atom U-238 would be 238/(6x10^23) = 39.7 x 10^-23 gram or more properly 3.97 x 10^-22 gram
Half-Life The “half-life” (h) is the time it takes for half the atoms of a radioactive substance to decay. For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after: Time #atoms remaining % of atoms remaining 1 hour ? 10,000 (50%) 2 hours ? 5,000 (25%) 3 hours ? 2,500 (12.5%)
Decay curves Example for; No = 100 nuclei T1/2 = 5 days Nuclei remaining as a function of time 100 80 60 40 20 5 10 15 Time (days)
See PhET alpha-decay applet
. Carbon Dating
How old is a piece of wood 3 half lives of C-14 since the time the tree died? Half life of C14 = 5730 years . 1 half life 1 half life 1 half life ? ? ? ? ? ?
See PhET radioactive-dating-game applet
After a tree dies, it no longer absorbs C-14 from the atmosphere. When the tree dies, the C-14 in it starts to decay. The half life of the isotope C -14 is 5700 years. A sample of a fossil tree has 1000 nuclei of C-14. How long ago did the tree die? A 5.7 years old B 4800 years old C 6800 years old D D not enough information Answer
After a tree dies, it no longer absorbs C-14 from the atmosphere. When the tree dies, the C-14 in it starts to decay. The half life of the isotope C -14 is 5700 years. A sample of fossil tree gives a radioactivity count of 625 counts per second. The moment the tree died its radioactivity count was 10000 counts per second. How long ago did the tree die? A 11400 years old B 22900 years old Answer C 900 years old D not enough information
After a tree dies, it no longer absorbs C-14 from the atmosphere. When the tree dies, the C-14 in it starts to decay. The half life of the isotope C -14 is 5700 years. A 5g sample of fossil tree gives a radioactivity count of 50 counts per second. The moment the tree died its radioactivity count was 1000 counts per second per gram. How long ago did the tree die? A 17000 years old B 23000 years old 35000 years old Answer C D not enough information